Radio communication system and communication control method

ABSTRACT

A radio communication system includes: a plurality of cells having different scrambling sequences, respectively, wherein at least two cells communicate with at lease two user terminals connected to different serving cells; and a controller which controls the plurality of cells and provides a single scrambling sequence to said at least two cells and said at least two user terminals for control signal transmission and reception.

BACKGROUND

The present invention relates generally to a radio communication systemand, more specifically, to techniques of control signal transmission incoordinated multi-point (CoMP) transmission/reception schemes.

Recently, LTE (Long Term Evolution)-Advanced standard has been developedfor 4th generation system (4G), where the fairly aggressive target insystem performance requirements have been defined, particularly in termsof spectrum efficiency for both downlink (DL) and uplink (UL) asindicated in the Sect. 8 of 3GPP TR 36.913 v9.0.0, Requirements forfurther advancements for Evolved Universal Terrestrial Radio Access(E-UTRA) (LTE-Advanced), December 2009 (hereinafter referred to as “NFL1”). Considering the target of the cell-edge user throughput and theaverage cell throughput, which is set to be roughly much higher thanthat of LTE Release 8 (Rel. 8), multiple techniques, such as carrieraggregation, downlink enhanced MIMO, coordinated multi-pointtransmission/reception (CoMP), have been included in LTE-Advanced.

In Rel. 8/9/10, the downlink control channel (PDCCH) is defined to sendcontrol signal in Sect. 6.8 of 3GPP TS 36.211 v10.3.0, Physical Channelsand Modulation for Evolved Universal Terrestrial Radio Access (E-UTRA)(Release 10) (hereinafter referred to as “NPL2”). Each UE's downlinkcontrol information (DCI) is aggregated into consecutive control channelelements (CCEs), where a control channel element corresponds to 9 REgroups as defined in Sect. 6.2.4 of NPL2. The DCI transports downlink oruplink scheduling information, requests for aperiodic CQI reports,notifications of uplink power control commands, etc. as described in theSect. 5.3.3 of 3GPP TS 36.212 v10.3.0, Multiplexing and channel codingfor Evolved Universal Terrestrial Radio Access (E-UTRA) (Release 10)(referred to as “NPL3”). The CCEs of multiple UEs connected to sameserving cell are multiplexed and then scrambled by using a scramblingsequence initialized by a value c_(init) at the start of each subframe,which is a function of physical-layer cell identity (ID) of the servingcell as defined in the following equation in the Sect. 6.8.2 of NPL2 forinterference randomization. In the following, the initialization valueof scrambling sequence generation is called as the scramblinginitialization value cinit for the sake of convenience.

c _(init) =└n _(s)/2┘2⁹ +N _(ID) ^(ServCell)  {Math. 1}

where n_(s) is the slot number within a radio frame.

The scrambled bit sequence is QPSK (Quadrature Phase ShiftKeying)-modulated and mapped to the resource elements of PDCCH. Theserving cell reserves a radio resource region for PDCCH of its UEs,i.e., whole bandwidth of first several OFDM symbols (max. 4 OFDMsymbols) in a subframe. With the assistance of blind detection at UEside, only the location of the reserved radio resource region isrequired to be known by UE. The information of the location of thereserved radio resource is dynamically indicated by using L1/L2 signalthrough such as physical control format indicator channel (PCFICH),defined in the Sect. 6.7 of NPL2.

The present PDCCH, demodulated by cell-specific reference signal (CRS),is sent only by the serving cell and always occupies the entire systembandwidth of the first several OFDM symbols. It is not flexible totailor the transmission characteristics of PDCCH to an individual UE andalso impossible to coordinate transmissions in the frequency domain.This makes PDCCH ill-suited for new deployment, where the notion of acell is less clear and where flexibility in how to transmit is needed tohandle unexpected interference situations. Due to unexpectedinterferences, PDCCH capacity becomes a bottleneck when applying carrieraggregation, downlink enhanced MIMO and CoMP, etc.

In order to eliminate such a bottleneck, enhanced PDCCH (ePDCCH) hasbeen proposed by R1-113155, Nokia (referred to as “NPL4”) and R1-113356,Ericsson, ST-Ericsson (referred to as “NPL5”). As shown in FIG. 1, theePDCCH is sent over allocated resource blocks (RBs) in physical downlinkdata channel (PDSCH) area to increase the capacity and coverage of thecontrol signal. The employment of UE-specific RS (DM-RS) in ePDCCHtransmission makes the transmission properties transparent to the UE. Inprinciple, the enhanced single-point MIMO as well as multi-point MIMO(i.e., CoMP) schemes for improving the throughput of data transmissionbecomes also available for the DL control signal transmission, as statedin NPL5. For the blind detection of ePDCCH at UE side, the location ofthe reserved radio resource region may be informed semi-statically(e.g., 120 ms, 240 ms, etc.) as the information element ofE-PDCCH-Config by RRC signaling, similar to the way to inform theconfiguration of the relay PDCCH (R-PDCCH) as introduced in the Sect.6.3.2 of 3GPP TS 36.331 v10.3.0, Radio resource control (RRC) andProtocol specification of Evolved Universal Terrestrial Radio Access(E-UTRA) (Release 10) (hereinafter referred to as “NPL6”).

For LTE-Advanced Rel. 11, CoMP has been agreed to be included as a toolto improve the coverage of high data rates, the cell-edge throughput,and also to increase system throughput as described in the Sect. 4 of3GPP TR 36.819 v11.0.0, Coordinated multi-point operation for LTEphysical layer aspects (Release 11) (hereinafter referred to as “NFL7”). The CoMP schemes, joint transmission (JT), dynamic point selection(DPS), and coordinated scheduling/coordinated beamforming (CS/CB) aresupposed to be supported as described in the Sect. 5.1.3 of NPL7. TheCoMP cooperating set is defined in the Sect. 5.1.4 of NPL7 as a set of(geographically separated) points directly and/or indirectlyparticipating in data transmission to a UE in time-frequency resource.In case of JT and DPS, UE's data, scrambled by a scrambling sequencewith the serving cell's scrambling initialization value as defined inthe Sect. 6.3.1 of NPL2, should be shared among more than one point inCoMP cooperating set; while, in case of CS/CB, data for a UE is onlyavailable at and transmitted from the one point (serving point) but userscheduling/beamforming decisions are made with coordinated among pointscorresponding to the CoMP cooperating set. It should be noted that theterm “point” for coordinated multi-point transmission/reception can beused as a radio station, a transmission/reception unit, remote radioequipment (RRE) or distributed antenna of a base station, Node-B or eNB.Accordingly, hereinafter, a point, a radio station, atransmission/reception unit and a cell may be used synonymously.

According to the performance evaluation results in Sect. 7 of NPL7,JT/DPS CoMP achieves better performance than CB/CS to improve thecell-edge user throughput of downlink data transmission. For a cell-edgeUE, which suffers from poor channel condition of serving point andstrong interference from CoMP point, JT/DPS CoMP can also be applied toimprove the capacity of its control signal in a similar way as that ofdata, by sharing not only data but also control signal, scrambled by ascrambling sequence with the serving cell's scrambling initializationvalue cinit among the selected transmission points (TPs).

A simple example of the above-described scheme is given in FIGS. 2A and2B. Assuming that UE1 and UE2 have Cell1 as serving cell and Cell2 asCoMP cell as shown in FIG. 2A, ePDCCH can aggregate control informationof the UE1 and UE2 using the same scrambling sequence for Cell1 andCell2 as shown in FIG. 2B. As described in Section 6.8.2 of the NPL2,the scrambling sequence generation is initialized with the followinginitialization value c_(init) determined by the ID of Cell1 (servingcell).

c _(init) =└n _(s)/2┘2⁹ +N _(ID) ^(Cell1)  {Math. 2}

In the case of the UE2 with a different serving cell, however, theaggregation of control signal with CoMP cannot be made because differentscrambling initialization values and different radio resources are usedfor the control signals of the UE1 and UE2, respectively. As shown inFIG. 3A, it is assumed that UE1 and UE2 are selected as CoMP UEs withmultiple cooperating cells and the UE1 has Cell1 as serving cell andCell2 102 as CoMP cell; while, the UE2 has Cell2 as the serving cell andCell1 as the CoMP cell. For the employment of JT/DPS CoMP, the controlsignal of UE1, scrambled by using the Cell2's scrambling initializationvalue, is shared by Cell2. On the other hand, the control signal of UE2,scrambled by using the Cell2's scrambling initialization value, isshared by Cell1. Accordingly, the scrambling sequence generation isinitialized with different initialization values c_(init1) and c_(init2)for Cell1 and Cell2, respectively:

c _(init1) =└n _(s)/2┘2⁹ +N _(ID) ^(Cell1)

c _(init2) =└n _(s)/2┘2⁹ +N _(ID) ^(Cell2)  {Math. 3}

Besides their different scrambling initialization values, differentradio resource regions are reserved at Cell1 and Cell2 for sending UE1'sand UE2's control signals, respectively as shown in FIG. 3B. Within thepreviously reserved radio resource region, the occupied resource isdynamically allocated, resulting in remained resource.

In FIG. 3B, as an example, separate resources with max 3RBs for each oneare reserved for each UE, but average 2RBs are used for each UE'scontrol signal. As a consequence, an increasing number of CoMP UEs withdifferent serving cells results in larger reserved radio resourceregions in multiple cooperating cells.

An object of the present invention is to provide a method and systemwhich can efficiently send control signals with improved capacity andcoverage of a control signal for UEs with different serving cells.

SUMMARY

According to the present invention, a radio communication systemincludes: a plurality of cells having different scrambling sequences,respectively, wherein at least two cells communicate with at lease twouser terminals connected to different serving cells; and a controllerwhich controls the plurality of cells and provides a single scramblingsequence to said at least two cells and said at least two user terminalsfor control signal transmission and reception.

According to the present invention, a method for controlling a pluralityof cells having different scrambling sequences in a radio communicationsystem, includes the steps of: setting at least two cells whichcommunicate with at lease two user terminals connected to differentserving cells; and providing a single scrambling sequence to said atleast two cells and said at least two user terminals for control signaltransmission and reception.

According to the present invention, a control device for controlling aplurality of cells having different scrambling sequences in a radiocommunication system, includes: a setting section for setting at leasttwo cells which communicate with at lease two user terminals connectedto different serving cells; and a communication controller for providinga single scrambling sequence to said at least two cells and said atleast two user terminals for control signal transmission and reception.

Advantageous Effects of Invention

According to the present invention, the reserved radio resource regionfor control signals for UEs with different serving cells can beeffectively reduced. In addition, the exchanging messages amongcooperating cells for the control signal of UEs also become less forcoordinating the distributed scheduling results of different cooperatingcells.

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of control signalconfiguration of PDCCH and enhanced PDCCH (ePDCCH).

FIG. 2A is a schematic diagram illustrating a radio communication systemhaving two UEs with same serving cell.

FIG. 2B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 2A.

FIG. 3A is a schematic diagram illustrating a radio communication systemhaving two UEs with different serving cells.

FIG. 3B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 3A.

FIG. 4A is a schematic diagram illustrating control signal configurationfor a CoMP UE group for explaining an outline of the present invention.

FIG. 4B is a schematic diagram illustrating the function configurationof a control unit to implement the control signal configuration of FIG.4A.

FIG. 5 is a diagram illustrating an example of a radio communicationsystem according to a first illustrative embodiment.

FIG. 6 is a diagram illustrating detailed functional configurations ofthe controller, TxRx units and UEs in the radio communication system ofFIG. 5.

FIG. 7 is a sequence diagram illustrating an example of operations ofradio communication system of FIG. 6.

FIG. 8A is a schematic diagram illustrating a first example of the radiocommunication system employing JT CoMP to ePDCCH and PDSCH for UE1 andUE2 according to the first illustrative embodiment.

FIG. 8B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 8A.

FIG. 9A is a schematic diagram illustrating a second example of theradio communication system employing DPS CoMP to ePDCCH and PDSCH forUE1 and UE2 according to the first illustrative embodiment.

FIG. 9B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 9A.

FIG. 10A is a schematic diagram illustrating a third example of theradio communication system employing JT CoMP to PDCCH and PDSCH for UE1and UE2 according to the first illustrative embodiment.

FIG. 10B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 10A.

FIG. 11A is a schematic diagram illustrating a fourth example of theradio communication system employing DPS CoMP to PDCCH and PDSCH for UE1and UE2 according to the first illustrative embodiment.

FIG. 11B is a schematic diagram illustrating the control signalconfiguration for each UE in the radio communication system of FIG. 11A.

FIG. 12 is a diagram illustrating an example of a radio communicationsystem according to a second illustrative embodiment.

FIG. 13 is a diagram illustrating detailed configurations of eNBs in theradio communication system of FIG. 12.

FIG. 14 is a sequence diagram illustrating an example of operations ofradio communication system of FIG. 13.

DETAILED DESCRIPTION

First, the general outlines of the present invention will be describedwith reference to FIGS. 4A and 4B.

As shown in FIG. 4A, multiple UEs (UE1, . . . UEn) with the same CoMPcooperating set but different serving cells are aggregated as a CoMP UEgroup with a single scrambling initialization value which is sharedamong cooperating cells of the CoMP cooperating set. A reserved resourceRrsv is determined so as to accommodate a total amount of resources forcontrol signals of the UE1-UEn in the CoMP UE group. The respectiveresources for control signals of the UE-UEn in the CoMP UE group aredynamically allocated within the reserved resource Rrsv and the controlsignals in the CoMP UE group are scrambled using the single scramblinginitialization value.

Referring to FIG. 4B, it is assumed that a core control unit controlsradio transmission and reception stations TxRx_1, . . . TxRx_n(hereinafter, referred to as TxRx units) which in turn control UE1-UEnwith different serving cells corresponding to the TxRx units,respectively. The core control unit performs: grouping the UE1-UEn withdifferent serving cells but the same CoMP cooperating set into a CoMP UEgroup; selecting the scrambling initialization value for the CoMP UEgroup; and reserving the shared resource Rrsv as shown in FIG. 4A.Thereafter, the core control unit performs coordinated scheduling andinforming control signal configuration to each TxRx unit. In this way,the information related to the scrambling initialization value and thereserved resource Rrsv is shared among the TxRx units and the UEs fortransmitting and receiving control signals.

As an example, considering that UE1 and UE2 are connected to differentserving cells (Cell1 and Cell2) but having the same CoMP cooperatingset, UE1 and UE2 can be grouped as a CoMP UE group. A common scramblinginitialization value is used for initializing the scrambling sequence oftheir control signal. In addition, the reserved resource region Rrsv forcontrol signal transmission can be set to 5RBs at Cell1 and Cell2, whereeach UE uses average 2RBs for sending DCI. In this case, the reservedresource region Rrsv is smaller than a total resource (6RBs) forseparate control signal transmission of the UE1 and UE2.

The illustrative embodiments will be explained by making references tothe accompanied drawings. The illustrative embodiments used to describethe principles of the present invention are by way of illustration onlyand should not be construed in any way to limit the scope of thedisclosure. Those skilled in the art will understand that the principlesof the present disclosure may be implemented in any suitably arrangedwireless network. In the present technical field related to radiocommunication systems, the terms “point”, “cell”, “radio station” and“transmission/reception (TxRx) unit” of a base station (Node-B or eNB)may have same meaning, so serving point and cooperating point can beinterpreted as serving cell and cooperating cell, serving TxRx unit andcooperating TxRx unit, or serving radio station and cooperating radiostation, respectively. Accordingly, in this disclosure, the term “cell”or “TxRx unit” is used appropriately.

1. First Illustrative Embodiment

According to the first illustrative embodiment, intra-eNB CoMP isapplied to control signal transmission. Detailed configuration andoperation will be described by referring to FIGS. 5-7.

1.1) System Configuration

As shown in FIG. 5, it is assumed that a network is composed of acontroller 10 and TxRx units 21 and 22 (or Cell1 and Cell2), to which aradio communication system according to the first illustrativeembodiment is applied. The controller 10 controls the TxRx units 21 and22 (or Cell1 and Cell2) through backhaul links BL1 and BL2,respectively. The UE1 and UE2 are communicating with the TxRx units 21and 22 through radio channels under the control of the network. Moredetailed configuration of the radio communication system will bedescribed below.

Referring to FIG. 6, the controller 10 includes the function blocks of:CoMP cooperating set selection section 101; CoMP UE grouping section102; scrambling initialization value selection section 103; resourcereservation section 104; scheduler 105; backhaul link (BL) communicationsection 106; and a control section 107. The TxRx units 21 and 22 havethe same functional configuration as follows: BL communication section211, 221; control section 212, 222; radio transmitter 213, 223; andradio receiver 214, 224. The BL communication sections 211 and 221 areconnected to the backhaul link (BL) communication section 106 throughthe backhaul links BL1 and BL2, respectively, so that data and controlsignal transmission/reception can be controlled by the controller 10.The UE1 and UE2 have the same functional configuration as follows: radiotransmitter 311,321; radio receiver 312, 322; DL signal detectionsection 313, 323; channel state information (CSI) estimation section314, 324; and controller 315, 325. Each cell (TxRx unit 21, 22) in CoMPcooperating set is communicating with the UE1 and UE2, which are alsoreferred to as CoMP UEs.

By using the above-mentioned function blocks, the CoMP cooperating setselection section 101 selects a CoMP cooperating set including more thanone cell (here, TxRx units 21 and 22) for each UE (here, UE1, UE2).Thereafter, the CoMP UE grouping section 102 groups the CoMP UEs withthe same CoMP cooperating set as a CoMP UE group. For sending thecontrol signal of such a CoMP UE group, the scrambling initializationvalue selection section 103 chooses a single scrambling initializationvalue and the resource reservation section 104 reserves the shared radioresource region Rrsv. Next, the scheduler 105 performs the jointscheduling of multiple cells belonging to the CoMP cooperating set,where the network dynamically selects the transmission point(s), TP(s),of TxRx unit(s), and on selected TP(s) allocates the RBs as well as REswithin the reserved resource region Rrsv for each UE in the CoMP UEgroup. In case of precoding at selected TP(s), the precoding matrixindex (PMI) as well as rank indicator (RI) for each UE needs to bedecided for each selected TP. The detailed process is described asfollows.

Referring to FIG. 7, at first, when the TxRx units 21 and 22 havereceived an uplink signal from the UE1 and UE2, respectively (operations401 and 402), the control sections 212 and 222 transmits informationindicating the received power of uplink sounding reference signal (SRS)or the UE feedback downlink reference signal received power (RSRP) tothe controller 10 through the BL communication section 211 and 221(operations 403 and 404). Based on the information indicating SRS poweror the RSRP, the CoMP cooperating set selection section 101 selects theCoMP cooperating set for each UE (operation 405). For example, a cell,whose RSRP difference relative to that of the serving cell is within athreshold, will be regarded as a CoMP cell. The UE having more than onecooperating cell is regarded as a cooperating cell (CoMP cell). It isfound that UE1 and UE2 are CoMP UEs, who have the same CoMP cooperatingset consisting of Cell1 and Cell2, although UE1's serving cell is Cell1and UE2's serving cell is Cell2.

The CoMP UE grouping section 102 groups UE1 and UE2 into one CoMP UEgroup (operation 406). For this CoMP UE group, the scramblinginitialization value selection section 103 selects a single scramblinginitialization value for the scrambling sequence of control signal,e.g., PDCCH or ePDCCH (operation 407). The scrambling initializationvalue can be determined by the ID of one CoMP cooperating cell, i.e.,Cell1's ID or Cell2's ID, or a different ID for the sake of interferencerandomization. For example, the scrambling sequence is initialized as acommon initialization value c_(init) for Cell1-Celln as follows:

$\begin{matrix}{c_{init} = {{\left\lfloor {n_{s}/2} \right\rfloor 2^{9}} + N_{ID}^{\underset{\_}{VIRTUAL}}}} & \left\{ {{Math}.\mspace{14mu} 4} \right\}\end{matrix}$

where N_(ID) ^(VIRTUAL) is a specific virtual cell ID for the CoMP UEgroup.

c _(init) =└n _(s)/2┘2⁹ +N _(ID) ^(ServCell) +N _(offset)  {Math. 5}

where N_(offset) is the ID offset for each UE belong to the CoMP UEgroup. N_(offset) is adjusted to obtain same cinit for each UE in CoMPUE group.

The control section 107 sends the virtual cell ID or cell ID offset,parameter of scrambling initialization value cinit, to the TxRx units 21and 22 (operations 408 and 409) for generating the CoMP UE group'scontrol signal, and the TxRx units 21 and 22 further send it to the UE1and UE2 as the information element of PDCCH-Config or E-PDCCH-Config byRRC signaling for detecting the control signal, respectively (operations410 and 411).

Next, the resource reservation section 104 reserves the shared radioresource region Rrsv (see FIG. 4A) at both Cell1 and Cell2 for applyingJT/DPS CoMP to control signal transmission (operation 412). The controlsection 107 notifies the TxRx units 21 and 22 of the location of theshared radio resource region Rrsv (operations 413 and 414)), whichfurther send it to the UE1 and UE2 (operations 415 and 416).

According to the feedback CSI by UE, the scheduler 105 firstly carriesout channel-dependent scheduling for data transmission and thereaftereach UE's DCI including dynamic scheduling results can be aggregatedinto consecutive CCEs (operation 417). For each UE in the CoMP UE group,the control section 107 selects transmission points (TxRx units) andallocates RBs and REs within the reserved radio resource region Rrsv. Incase of precoding, the PMI as well as RI for each selected TP of theCoMP UE are also decided, respectively. For control signal transmission,besides the virtual cell ID or cell ID offset for scramblinginitialization value cinit, the control section 107 also informs eachselected TxRx unit, through a corresponding backhaul link, of dynamicscheduling results which includes the aggregated CCE number, thepositions of allocated RBs and REs as well as PMI and RI for precoding(operations 418 and 419).

The virtual cell ID or cell ID offset for generating the scramblinginitialization value c_(init) of the CoMP UE group may be indicatedsemi-statically, e.g., 120 ms, 240 ms, etc.; while, the dynamicscheduling results need to be updated more frequently, e.g., with aperiod of 5 ms, 10 ms, etc. Accordingly, each of the control sections212 and 222 generates the control signal of the CoMP UE group bymultiplexing the CCEs of the UE1's DC1 and UE2's DCI at first and thenscrambling the bit sequence by using the scrambling initialization valuecinit with the informed virtual cell ID or cell ID offset (operations420 and 421). After that, the transmitter 213, 223 of a correspondingTxRx unit modulates the scrambled bit sequence and maps the modulatedsignal on the allocated REs within the allocated RBs to send the controlsignal of the CoMP UE group.

As described above, for control signal detection at UE side, the controlsection 107 informs each UE in the CoMP UE group of the virtual cell IDor cell ID offset for generating the scrambling initialization valuecinit as well as the location of the reserved radio resource regionRrsv. The signal related to the virtual cell ID or cell ID offset of thescrambling initialization value cinit and the signal related to thelocation of reserved radio resource region Rrsv may be sentsimultaneously or independently. For example, the information of thescrambling initialization value cinit together with the location ofreserved radio resource region Rrsv may be included in the informationelements of PDCCH-Config or E-PDCCH-Config by RRC signaling andsemi-statically indicated through PDSCH of serving cell with a period of120 ms, 240 ms, etc. At the UE side, the blind detection within theinformed reserved region Rrsv is carried out to detect the controlsignal. In another way, the location of radio resource region Rrsv maybe dynamically sent to the UE by using L1/L2 signal with a period of 5ms, 10 ms, etc., independently from that of the scramblinginitialization value cinit. For example, for PDCCH, the reserved regionRrsv is the first several OFDM symbols and the number of the OFDMsymbols for PDCCH is dynamically informed to UE by using the L1/L2signal through PCFICH, which includes the information of the length ofRrsv for PDCCH. For ePDCCH, the start position of ePDCCH can besemi-statically informed by using RRC signal and the length of Rrsv forePDCCH can be dynamically informed to UE by using the L1/L2 signalthough enhanced PCFICH at the beginning of ePDCCH, which carries theinformation of the length of the ePDCCH resource. Or, the dynamicsignaling of the region Rrsv for ePDCCH is informed to UE through itsserving cell's PDCCH. In this case, the UE firstly detects the PDCCH toobtain the location of the region Rrsv and then detects the ePDCCHwithin the region Rrsv. Thereafter, the blind detection may be avoidedat the price of larger signaling overhead for the information in PDCCH.The detailed examples are given below.

With the knowledge of the virtual cell ID or cell ID offset forscrambling initialization value cinit and the reserved resource regionRrsv, the DL signal detection section 313, 323 of each UE can detect thecontrol signal, by demapping the received signal, demodulating thesymbol sequence, and then descrambling the bit sequence (operations 422and 423). Hereafter, the UE1's DC1 and UE2's DCI are blindly detected inthe informed reserved resource region Rrsv, respectively.

According to each UE's DCI associated with the downlink transmission,the CSI estimation section 314, 324 can further detect its receiveddownlink data in PDSCH as well as the downlink reference signal for CSIestimation. According to the UE's DCI associated with the uplinktransmission, the control section 315, 325 generates the uplink data andsends over physical uplink shared channel (PUSCH) from each UE'stransmitter 311, 321. In addition, the control section 315, 325generates the feedback CSI together with other uplink controlinformation and sends over physical uplink control channel (PUCCH).

1.2) First Example

A first example of the communication control method according to thefirst illustrative embodiment shows the case of ePDCCH with JT CoMP,which will be described by referring to FIGS. 8A and 8B.

As shown in FIG. 8A, JT CoMP is applied to send ePDCCH of CoMP UE groupfrom multiple selected TPs (TxRx units 21 and 22). Here, JT CoMP is alsoapplied to data transmission over PDSCH for UE1 and UE2. The TxRx units21 and 22 (Cell1 and Cell2) are the selected TPs, simultaneouslytransmitting both data and control signal to UE1 and UE2. For ePDCCH, acommon scrambling initialization value cinit is needed and a commonradio resource region Rrsv is reserved for UE1 and UE2.

As shown in FIG. 8B, over reserved resource region Rrsv, same RBs aswell as REs are allocated for each UE's DCI at both Cell1 and Cell2(TxRx units 21 and 22). In case of precoding of joint transmission, thePMI and RI at Cell1 and Cell2 need to be decided based on the UEfeedback CSI. For ePDCCH generation, the information of the commonscrambling initialization value cinit and the above dynamic schedulingresults is indicated to each selected TxRx unit over a correspondingbackhaul link BL. For ePDCCH detection, only the information related tothe common scrambling initialization value cinit (i.e., virtual cell IDor cell ID offset for the CoMP UE group) together with the location ofreserved resource region Rrsv is needed for the sake of blind detectionat the UE side.

1.3) Second Example

A second example of the communication control method according to thefirst illustrative embodiment shows the case of ePDCCH with DPS, whichwill be described by referring to FIGS. 9A and 9B.

As shown in FIG. 9A, DPS CoMP is applied to send ePDCCH of the CoMP UEgroup from one dynamically selected TP (TxRx unit). The process issimilar to that of ePDCCH with JT CoMP given in FIGS. 8A and 8B, exceptthat only one TP(TxRx unit) is dynamically selected for sending PDSCHand ePDCCH. Although the common radio resource region Rrsv is reservedat both Cell1 and Cell2 (TxRx units 21 and 22), the control section 107only allocates RBs and REs within the reserved radio resource regionRrsv at each UE's selected TP (TxRx unit).

As shown in FIG. 9B, 1the UE1's data and DCI is sent from the TxRx unit21 (Cell1); while the UE2's data and DCI is sent from the TxRx unit 22(Cell2) at a current subframe. In another subframe, it is possible thatthe UE1's data and DCI is sent from the TxRx unit 22 (Cell2) but theUE2's data and DCI is sent from TxRx unit 21 (Cell1). The selected TP(TxRx unit) may be dynamically updated with a period of 5 ms, 10 ms,etc. For ePDCCH generation, the information related to the commonscrambling initialization value cinit and the above dynamic schedulingresults are indicated to the UE's selected TP (TxRx unit) over acorresponding backhaul link BL. For ePDCCH detection at the UE side,only the information of the common scrambling initialization value cinitand the location of reserved resource region Rrsv are needed.

As illustrated in above example of ePDCCH with JT/DPS CoMP, only thelocation of reserved resource region Rrsv needs to be informed to UEsemi-statically for blind detection of control signal. It is alsopossible to semi-statically inform the start position of ePDCCH butdynamically send the length of reserved resource region Rrsv, such asthe number of RBs for Rrsv, in a L1/L2 signal through such as enhancedPCFICH (ePCFICH), which carries information about the number of RBs,used for transmission of ePDCCH in a subframe. To avoid blind detection,the aggregation level (i.e., number of aggregated CCEs) and the positionof the allocated RBs and/or REs may be informed directly by using aL1/L2 signal over PDCCH, at the price of higher signaling overhead.

1.4) Third Example

A third example of the communication control method according to thefirst illustrative embodiment shows the case of PDCCH with JT CoMP,which will be described by referring to FIGS. 10A and 10B.

As shown in FIG. 10B, JT CoMP is applied to send PDCCH of the CoMP UEgroup from multiple selected TPs (TxRx units 21 and 22). The process issimilar to that of ePDCCH with JT CoMP given in FIGS. 8A and 8B, exceptthat the allocated resources are restricted to the first several OFDMsymbols in case of PDCCH. Since the CRS and PCFICH with cell-specificshift occupy the REs also in the first OFDM symbols, the UE1's DC1 andUE2's DCI may be mapped to the REs without conflict with the CRS andPCFICH of Cell1 and Cell2. For PDCCH generation, the virtual cell ID orcell ID offset for common scrambling initialization value cinit, theOFDM index as well as the aggregation level and the position ofallocated RBs/REs for each UE needs to be known at each selected TP(TxRx unit). For PDCCH detection, the virtual cell ID or cell ID offsetfor common scrambling initialization value cinit is informedsemi-statically to each UE of PDCCH-Config or E-PDCCH-Config by RRCsignaling; while, the location of the reserved resource region Rrsv isindicated dynamically through PCFICH, which carries information aboutthe number of OFDM symbols, used for transmission of PDCCH in asubframe. As shown in FIG. 10B, the data and DCI of UE1 and UE2 aresimultaneously transmitted by Cell1 and Cell2 (TxRx units 21 and 22)over allocated RBs and REs in the shared reserved OFDM symbols. The UE1and UE2 can detect its own DCI by blind detection within the informedregion Rrsv of PDCCH.

1.5) Fourth Example

A fourth example of the communication control method according to thefirst illustrative embodiment shows the case of PDCCH with DPS, whichwill be described by referring to FIGS. 11A and 11B.

As shown in FIG. 11A, DPS CoMP is applied to send PDCCH of the CoMP UEgroup from a dynamically selected TP (TxRx unit). The process is similarto that of PDCCH with JT CoMP given in FIGS. 10A and 10B, except thatonly one TP (TxRx unit) is dynamically selected in a subframe forsending PDSCH and PDCCH. Although the common radio resource region Rrsvis reserved at both Cell1 and Cell2 (TxRx units 21 and 22), the controlsection 107 only allocates the RBs and REs within the reserved radioresource region Rrsv at each UE's selected TP (TxRx unit).

As shown in FIG. 11B, the UE1's data and DCI is sent from Cell1 (TxRxunit 21); while the UE2's data and DCI is sent from Cell2 (TxRx unit 22)at current subframe. In another subframe, it is possible that the UE1'sdata and DCI is sent from Cell2 (TxRx unit 22) but the UE2's data andDCI is sent from Cell1 (TxRx unit 21). The selected TP (TxRx unit) maybe dynamically updated with a period of 5 ms, 10 ms, etc. For PDCCHgeneration, the information related to the common scramblinginitialization value cinit and the above dynamic scheduling results isindicated to the UE's selected TP (TxRx unit). For PDCCH detection, thevirtual cell ID or cell ID offset for common scrambling initializationvalue cinit for the CoMP UE group is informed semi-statically to each UEof PDCCH-Config or E-PDCCH-Config by RRC signalling; while, the locationof the reserved resource region Rrsv, i.e. the number of OFDM symbolsfor PDCCH, is indicated dynamically as a L1/L2 signal through PCFICH.

1.6) Other Examples

In the above-described examples as shown in FIGS. 8-11, the same CoMPscheme by using same selected TP(s) is used to send the downlink dataover PDSCH and the downlink control signal over ePDCCH or PDCCH.However, the CoMP scheme as well as TP(s) can be independently decidedfor control signal and data transmission. For example, JT is used fordata transmission but DPS is used for control signal transmission,considering the limited radio resources.

2. Second Illustrative Embodiment

According to the second illustrative embodiment, inter-eNB CoMP isapplied to control signal transmission. Detailed configuration andoperation will be described by referring to FIGS. 12-14.

As shown in FIG. 12, eNB1 and eNB2 are connected by X2 backhaul link.Each eNB includes the same functions as those of the controller 10 asshown in FIG. 6. More specifically, as shown in FIG. 13, Each eNB isprovided with BL communication section (211, 221), radio transmitter(213, 223); radio receiver (214, 224); and control section (210, 220).The control section (210, 220) has not only the functions for eNBoperations as described before but also the functions for inter-eNB CoMPapplied to control signal transmission. The BL communication sections211 and 221 are connected to each other through the X2 backhaul link,allowing the inter-eNB CoMP for control signal transmission. Otherfunction blocks similar to those described with reference to FIG. 6 aredenoted by the same reference numerals and their detailed descriptionsare omitted.

By using the above-mentioned function blocks, the control section 210,220 can find the CoMP UEs connected to eNB1 and eNB2, respectively. TheUE1 has serving eNB1 and cooperating eNB2; while the UE2 has servingeNB2 and cooperating eNB1. By exchanging information over the X2backhaul link, the CoMP UEs with the same CoMP cooperating set aregrouped at each eNB. For control signal transmission of the UE1 and UE2,the common scrambling initialization value cinit is chosen and theshared radio resource region Rrsv is reserved. More specifically, theoperations of the control sections 210 and 220 will be described byreference to FIG. 14.

Referring to FIG. 14, at first, when the eNB1 and eNB2 have received anuplink signal from the UE1 and UE2, respectively (operations 501 and502), the control sections 210 and 220 use information of the receivedpower of uplink sounding reference signal (SRS) or the UE feedbackdownlink reference signal received power (RSRP) to select the CoMPcooperating set for each UE (operations 503.1, 503.2). After exchangingthe information related to each UE's CoMP cooperating set through X2backhaul between sections 211 and 221, the control sections 210 and 220group UE1 and UE2 into one CoMP UE group (operations 504.1, 504.2). Forthis CoMP UE group, the control sections 210 and 220 select a virtualcell ID or cell ID offset for determining the same scramblinginitialization value cinit for ePDCCH of each UE in the CoMP UE group(operations 505.1, 505.2). The virtual cell ID or cell ID offset can bethe same as the ID of one CoMP cooperating cell, i.e., Cell1's ID orCell2's ID, or a different ID for the sake of interferencerandomization. The control sections 210 and 220 send the virtual cell IDor cell ID offset to the UE1 and the UE2, respectively (operations 506and 507). The scrambling sequence is initialized by a commoninitialization value c_(init) for Cell1 and Cell2 as described before.

Next, by exchanging the information over X2 backhaul, the controlsections 210 and 220 reserve the shared radio resource region Rrsv (seeFIG. 4A) at both Cell1 and Cell2 for control signal transmission(operations 508.1, 508.2). The control sections 210 and 220 notify theUE1 and UE2 of the location of the shared radio resource region Rrsv(operations 509 and 510).

Next, the control sections 210 and 220 perform the distributedscheduling at eNB1 and eNB2, respectively (operations 511.1, 511.2).Each control section of the eNB1 and eNB2 dynamically assigns theresources for each UE connected to the corresponding eNB. In case ofprecoding, the PMI as well as RI for each UE needs to be decided. Bycoordinating the results of distributed scheduling through the X2backhaul link, the control sections 210 and 220 corporate each other forthe data transmission with JT/DPS CoMP. After that, each UE's DCIincluding the dynamic scheduling results can be aggregated intoconsecutive CCEs.

For the UE in the CoMP UE group, each eNB allocates the RBs and REswithin the reserved radio resource region Rrsv. By exchanging theinformation over the X2 backhaul link, the coordination amongcooperating eNBs is needed for control signal transmission with JT/DPSCoMP. In case of JT CoMP, the same RBs as well as REs are allocated ateNB1 and eNB2 for UE1 and UE2, respectively. In case of DPS, the RBs andREs at one selected eNB is allocated to achieve largest data rate. Forcoordinating the distributed scheduling results of different cooperatingcells, the exchanging messages for the aggregated control signal of aCoMP UE group is relatively smaller than that of separate control signalfor different CoMP UEs.

Accordingly, each of the control sections 210 and 220 generates thecontrol signal of the CoMP UE group by multiplexing the CCEs of theUE1's DC1 and UE2's DCI first and then scrambling the bit sequence byusing the informed virtual cell ID or cell ID offset for generating samescrambling initialization value cinit for the CoMP UE group (operations512 and 513).

With the knowledge of the virtual cell ID or cell ID offset forscrambling initialization value cinit and the reserved resource regionRrsv, each UE can detect the control signal, by demapping the receivedsignal, demodulating the symbol sequence, and then descrambling the bitsequence (operations 514 and 515). Hereafter, the UE1's DC1 and UE2'sDCI are blindly detected in the informed reserved resource region Rrsv,respectively. The detailed process of the employment of JT/DPS CoMP onePDCCH and PDCCH is similar to that of the first to fourth examples,which is not redundantly described here.

3. Additional Statements

The present invention can be applied to a mobile communications systememploying coordinated transmission among multiple points to send controlsignal to multiple UEs.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Theabove-described illustrative embodiment and examples are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims ratherthan by the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein. Part or all of the above-described illustrativeembodiments can also be described as, but are not limited to, thefollowing additional statements.

REFERENCE SIGNS LIST

-   10 controller-   21, 22 transmission/reception (TxRx) unit-   UE1, UE2 user equipment (user terminal)-   101 CoMP cooperating set selection section-   102 CoMP UE grouping section-   103 scrambling initialization value selection section-   104 resource reservation section-   105 scheduler-   106 backhaul link (BL) communication section-   107 control section-   210, 220 control section-   211, 221 BL communication section-   212, 222 control section-   213, 223 transmitter-   214, 224 receiver-   311, 321 transmitter-   312, 322 receiver-   313, 323 DL signal detection section-   314, 324 CSI estimation section

1. A radio communication system comprising: a plurality of cells havingdifferent scrambling sequences, respectively, wherein at least two cellscommunicate with at least two user terminals connected to differentserving cells; and a controller which controls the plurality of cellsand provides a single scrambling sequence to said at least two cells andsaid at least two user terminals for control signal transmission andreception.
 2. The radio communication system according to claim 1,wherein control signals of said at least two user terminals arescrambled using the single scrambling sequence in said at least twocells and said at least two user terminals.
 3. The radio communicationsystem according to claim 1, wherein the controller allocates a reservedradio resource region for control signals of said at least two userterminals.
 4. The radio communication system according to claim 3,wherein the controller dynamically allocates resources for controlsignals of said at least two user terminals within the reserved radioresource region.
 5. The radio communication system according to claim 1,wherein each of a plurality of cells is generated by atransmission/reception unit which is controlled by the controller. 6.The radio communication system according to claim 5, wherein said atleast two user terminals share a coordinated multipoint (CoMP)cooperating set which is a set of geographically separatedtransmission/reception units directly or indirectly participating inuser data transmission in a time-frequency resource.
 7. The radiocommunication system according to claim 5, wherein the controllerallocates a reserved radio resource region for control signals of saidat least two user terminals, wherein the controller simultaneously orindependently sends a first signal for sharing the single scramblingsequence and a second signal for sharing a location of the reservedradio resource region among said at least two user terminals.
 8. Theradio communication system according to claim 1, wherein the singlescrambling sequence is generated from a predetermined initializationvalue.
 9. The radio communication system according to claim 8, wherein apredetermined parameter for determining the predetermined initializationvalue is an identity different from cell identities of said at least twocells.
 10. The radio communication system according to claim 8, whereinthe predetermined parameter for determining the predeterminedinitialization value is an identity identical to one selected from cellidentities of said at least two cells.
 11. The radio communicationsystem according to claim 1, wherein a plurality oftransmission/reception units generating respective ones of the pluralityof cells is provided in a base station of the radio communicationsystem.
 12. The radio communication system according to claim 1, whereina plurality of transmission/reception units generating respective onesof the plurality of cells is provided in different base stations of theradio communication system.
 13. A method for controlling a plurality ofcells having different scrambling sequences in a radio communicationsystem, comprising: setting at least two cells which communicate with atlease two user terminals connected to different serving cells; andproviding a single scrambling sequence to said at least two cells andsaid at least two user terminals for control signal transmission andreception.
 14. The method according to claim 13, further comprising:scrambling control signals of said at least two user terminals using thesingle scrambling sequence in said at least two cells and said at leasttwo user terminals.
 15. The method according to claim 13, furthercomprising: allocating a reserved radio resource region for controlsignals of said at least two user terminals.
 16. The method according toclaim 15, wherein resources for control signals of said at least twouser terminals are dynamically allocated within the reserved radioresource region.
 17. The method according to claim 13, wherein each ofthe plurality of cells is generated by a transmission/reception unitwhich is controlled by the controller.
 18. The method according to claim17, wherein said at least two user terminals share a coordinatedmultipoint (CoMP) cooperating set which is a set of geographicallyseparated transmission/reception units directly or indirectlyparticipating in user data transmission in a time-frequency resource.19. The method according to claim 17, further comprising: allocating areserved radio resource region for control signals of said at least twouser terminals; and simultaneously or independently sending a firstsignal for sharing the single scrambling sequence and a second signalfor sharing a location of the reserved radio resource region among saidat least two user terminals.
 20. The method according to claim 13,wherein the single scrambling sequence is generated from a predeterminedinitialization value.
 21. The method according to claim 20, wherein apredetermined parameter for determining the predetermined initializationvalue is an identity different from cell identities of said at least twocells.
 22. The method according to claim 20, wherein the predeterminedparameter for determining the predetermined initialization value is anidentity identical to one selected from cell identities of said at leasttwo cells.
 23. The method according to claim 13, wherein a plurality oftransmission/reception units generating respective ones of the pluralityof cells is provided in a base station of the radio communicationsystem.
 24. The method according to claim 13, wherein a plurality oftransmission/reception units generating respective ones of the pluralityof cells is provided in different base stations of the radiocommunication system.
 25. A control device for controlling a pluralityof cells having different scrambling sequences in a radio communicationsystem, comprising: a setting section for setting at least two cellswhich communicate with at least two user terminals connected todifferent serving cells; and a communication controller for providing asingle scrambling sequence to said at least two cells and said at leasttwo user terminals for control signal transmission and reception. 26.The control device according to claim 25, wherein the communicationcontroller scrambles control signals of said at least two user terminalsusing the single scrambling sequence in said at least two cells and saidat least two user terminals.
 27. The control device according to claim25, further comprising: a resource reservation section for allocating areserved radio resource region for control signals of said at least twouser terminals.
 28. The control device according to claim 27, whereinthe resource reservation section dynamically allocates resources forcontrol signals of said at least two user terminals within the reservedradio resource region.
 29. The control device according to claim 25,wherein each of the plurality of cells is generated by atransmission/reception unit.
 30. The control device according to claim29, wherein said at least two user terminals share a coordinatedmultipoint (CoMP) cooperating set which is a set of geographicallyseparated transmission/reception units directly or indirectlyparticipating in user data transmission in a time-frequency resource.31. The control device according to claim 29, wherein the resourcereservation section allocates a reserved radio resource region forcontrol signals of said at least two user terminals, wherein thecommunication controller simultaneously or independently sends a firstsignal for sharing the single scrambling sequence and a second signalfor sharing a location of the reserved radio resource region among saidat least two user terminals.
 32. The control device according to claim25, wherein the single scrambling sequence is generated from apredetermined initialization value.
 33. The control device according toclaim 32, wherein a predetermined parameter for determining thepredetermined initialization value is an identity different from cellidentities of said at least two cells.
 34. The control device accordingto claim 32, wherein the predetermined parameter for determining thepredetermined initialization value is an identity identical to oneselected from cell identities of said at least two cells.
 35. Thecontrol device according to claim 25, wherein a plurality oftransmission/reception units generating respective ones of the pluralityof cells is provided in a base station of the radio communicationsystem.
 36. The control device according to claim 25, wherein aplurality of transmission/reception units generating respective ones ofthe plurality of cells is provided in different base stations of theradio communication system.
 37. A base station which communicates withat least one user terminal in its own cell, comprising: a settingsection for setting at least one other cell as a cooperating cell inwhich at least one other user terminal is connected to the at least oneother cell as a serving cell; and a communication controller forproviding a single scrambling sequence to its own cell, said at leastone cell, said at least one user terminal and said at least one otheruser terminal, for control signal transmission and reception.